But I notice that when I generate 400 'Bad Request' errors that LSWS handles with an internal 'built-in' error message, the error is not logged anywhere in the system in any error log or access log at all.

But if I generate for example 405 'Method Not Allowed' or 301 'Moved Permanently' errors they get logged OK alongside 404's, but 400's do not get logged. Eg if I sequentially generated a 405, 301 and then a 400 error, this is all I'd see in the access log:

The problem with requests end up with 400 code is that LSWS does not process the request any further to determine which vhost it belongs to, so it is not likely going into the respective vhost access log, it could be logged into the server access log as unclassified requests though.

Thanks for the reply. If any 400 errors get logged in the server log at all under LSWS, I can't find them

I guess that logging of failed requests of all HTTP types is probably - in general - potentially useful to web managers. It can tell you things about your site, your client's requests, or your referrers that could be handy to know from a diagnostic perspective.

400 errors can also alert you to some types of web attacks or probes, which may also be useful news to an administrator ...

So my personal vote would be for LSWS to figure out a way of logging them somewhere.